1. Field of the Invention
The present invention generally concerns fluid pressure brake and analogous systems and more particularly concerns multiple fluid receiving points involving front and rear brake pressure modifying.
2. Discussion of the Prior Art
Generally, brake pressure distribution (BPD) valves predeterminately control pressurized fluid to vehicle brakes to vary vehicle brake torque distribution dependent on vehicle deceleration levels. Valves of this type are for the purpose of providing substantially equal pressure distribution to the front and rear brakes when the brake system is operating below a certain predetermined pressure. This type of valve is compatible with a brake system having front and rear axle drum brakes.
Due to the use of shoe return springs, drum brakes require an initial pressure to overcome the opposing forces of the shoe return springs before any braking action occurs. Disc brakes generally do not have such return springs and therefore do not require the initial pressure to overcome such spring forces. As a result, when exposed to the same applied pressure, disc brakes will initially respond to applied pressure faster than drum brakes. Therefore, in a hybrid braking system, such as one including front axle disc brakes and rear axle drum brakes, equal pressure distribution below certain predetermined pressures is undesirable since the faster initial response to pressure application of the disc brakes would result in an initial imbalance of braking force between the front and rear brakes. That is, the front axle disc brakes would initially respond to applied pressure prior to a similar response by the rear axle drum brakes thus creating the possibility of initial front disc brake application prior to the rear drum brake application. Such imbalance could cause premature front axle lock-up on low friction road surfaces and could also cause a higher front brake wear rate.
To overcome these undesirable effects, it would be beneficial to provide unequal brake pressure distribution below certain predetermined pressures by providing a valve capable of initially delaying or restricting the pressure application to the front disc brakes while permitting unrestricted pressure application to the rear drum brakes to overcome the opposing force of the return springs. The desired result would be substantially simultaneous application of both the front disc and rear drum brakes.